Mail.Ru Group, the biggest russian internet company has a lot of Perl inside its main assets (web mail, social network). MRG is also the biggest publicly traded internet company in Europe. Other big russian companies like Yandex and Rambler also rely on Perl code heavily both for new and old projects.
Blekko is Perl and XS; I believe DuckDuckGo is Perl as well.
I can add (now that I work there) WhiteHat Security to that list (though we're quite promiscuous: I've done stuff in Python, Java and Mono there as well), and an awful lot of infrastructure is done in Perl at Yahoo!.
In Southern California we have Ticketmaster, Oversee.net, Rent.com, ValueClick, Shopzilla, PriceGrabber, Rubicon, MediaTemple, and Yahoo (ex-Overture) just that I know of personally. We have lots of smaller shops too, of course.
Adam J. Foxson, Lead Engineer, Infrastructure and Arc...(more)Lead Engineer, Infrastructure and Architecture, for CombineNet Inc., is a CPAN author, speaker at Perl venues, and has worked professionally with Perl for well over a decade.
Apple, large in terms of market capitalization, has 128 open positions that reference the keyword "Perl" at the time of the writing. The positions are in areas including but not limited to: automation, build engineering, QA, web development, tools, systems administration, infrastructure and integration. Accordingly, it may be reasonable to conclude that Apple, while not using Perl for the underlying architecture of core products and services, does use Perl (amongst a great many other technologies) as part of the underlying architecture of various internal systems and processes which are in support of their core products and services.
Grant Street Group, large in terms of auction volume, recently surpassed 11 trillion USD. Perl is the implementation language of their flagship platform.